Why does Object.assign not copy the properties of a URL object?

Question

On macOS 10.13.1 with Chrome 63.

I'm using Object.assign with new URL() as the source object but it always gives an empty object? This seems like strange behavior. Here is my code:

 let url = new URL('http://www.yahoo.com');
 console.log(url);
 let data = Object.assign({}, url);
 console.log(data);

Why is data an empty object whereas url has the complete URL object as below:

{
 href: "http://www.yahoo.com/", 
 origin: "http://www.yahoo.com", 
 protocol: "http:", 
 username: "", 
 password: ""
 ...
}

I also tried:

let data = Object.assign({}, ...url);  

but it gives:

Uncaught TypeError: undefined is not a function

Answer 1

I suspect it's because the properties of URL are not enumerable. Notice when you do Object.keys(url) you also get a blank array? Both Object.assign and Object.keys work with enumerable properties.

Properties on your url object are not enumerable.